Plain language

The authors provide these statistics: "Of the more than 700,000 students in [the Los Angeles Unified School District], more than 40% don't speak English as their native language. Of those, 94% are Spanish speakers, and the vast majority are native-born U.S. citizens."

Please explain how a U.S.-born fifth grader, living and being educated in the U.S., can be considered a "non-native speaker" of English? And how in the world do these children get all the way to the No Child Left Behind tests and still need to learn English?